System for reduction of harmful exhaust emissions from diesel engines

ABSTRACT

Methods and apparatus for reducing the TPM level of a diesel engine exhaust stream by providing a suitable oxidation catalyst into the exhaust train. The oxidation catalyst may be incorporated into a thermal insulative coating on the inner surface of the exhaust train, particularly the exhaust manifold and exhaust pipes prior to the turbocharger. Alternatively, when the exhaust train includes a turbocharger, the catalyst can be in a separate monolithic unit between the engine and the turbocharger. The system may also include an improved diesel oxidation catalyst unit having a metal monolithic substrate. The oxidation catalyst can also be incorporated into a thermal insulative coating inside the cylinders, particularly on non-rubbing surfaces such as The invention also includes the use of a protective mullite top coat on the thermal coating. A further embodiment is the use of a stainless steel bond coat to bind the thermal coating to a metallic substrate, particularly an aluminum substrate.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. Ser. No.08/635,345, filed Apr. 19, 1996.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a system for the reduction of harmfulexhaust emissions from diesel engines, and more particularly to a systemfor increasing the effectiveness of the oxidation of the oxidizablecomponents in the exhaust emissions.

[0004] 2. Description of Related Art

[0005] Diesel engine exhaust is a heterogeneous mixture which containsnot only gaseous emissions such as carbon monoxide (“CO”), unburnedhydrocarbons (“HC”) and nitrogen oxides (“NO_(x)”), but also condensedphase materials (liquids and solids) which constitute the so-calledparticulates or particulate matter (“PM”). The total particulate matter(“TPM”) emissions are comprised of three main components. One componentis the solid, dry, solid carbonaceous fraction or soot. This drycarbonaceous matter contributes to the visible soot emissions commonlyassociated with diesel exhaust. A second component of the TPM is thesoluble organic fraction (“SOF”). The soluble organic fraction issometimes referred to as the volatile organic fraction (“VOF”), whichterminology will be used herein. The VOF may exist in diesel exhausteither as a vapor or as an aerosol (fine droplets of liquid condensate)depending on the temperature of the diesel exhaust, and are generallypresent as condensed liquids at the standard particulate collectiontemperature of 52° C. in diluted exhaust, as prescribed by a standardmeasurement test, such as the U.S. Heavy Duty Transient Federal TestProcedure, discussed further below. These liquids arise from twosources: (1) lubricating oil swept from the cylinder walls of the engineeach time the pistons go up and down; and (2) unburned or partiallyburned diesel fuel.

[0006] The third component of the particulates is the so-called sulfatefraction. Diesel fuel contains sulfur, and even the low sulfur fuelavailable in the U.S. may contain 0.05% sulfur. Upon combustion of thefuel in the engine, nearly all of the sulfur is oxidized to sulfurdioxide which exits with the exhaust in the gas phase. However, a smallportion of the sulfur, perhaps 2-5%, is oxidized further to SO₃, whichin turn combines rapidly with water in the exhaust to form sulfuric acidwhich collects as a condensed phase with the particulates as an aerosol,or is adsorbed onto the other particulate components, and thereby addsto the mass of TPM.

[0007] Emissions from diesel engines have been under increasing scrutinyin recent years and standards, especially for particulate emissions,have become stricter. In 1994 the particulate emission standards in theU.S. for new engines allowed no more than a total of 0.1 grams per brakehorse power hour (g/BHP-h). For diesel engines in buses operating incongested urban areas the particulate emissions standard was evenstricter, 0.07 g/BHP-h TPM. Both of these standards were seen assignificant reductions relative to the prior particulate emissionstandard of 0.25 g/BHP-h which had been in effect since 1991. Startingin 1994, for the first time, engine technology developments alone werefound to be incapable of meeting the new standards, and for some enginesaftertreatment technology, for example, diesel oxidation catalyst (DOC)units, as discussed further below, were necessary.

[0008] Current engines are generally capable of meeting the 1994 NO_(x)emissions standards of 5.0 g/BHP-h, but by only a slim margin. Dieselengines, because they operate with a great excess of combustion air(lean exhaust) typically have emissions of CO and gas phase HC's whichare well below the 1994 emissions standards of 15.5 g/BHP-h and 1.3g/BHP-h, respectively. Therefore, the key emission control concerns fordiesel engines now and for the immediate future are the reduction inparticulates (TPM) and NO_(x) emissions.

[0009] Emissions of NO_(x) from diesel engines can be reduced byretarding injection timing. However, this is accompanied by acorresponding increase in particulate emissions, particularly of the drycarbon or soot portion. Emissions of NO_(x) can also be reduced byapplying exhaust gas recirculation (EGR) technology. However, this isalso accompanied by a corresponding increase in particulate emissions.Thus, both of these engine technologies are constrained by a trade-offor balance between TPM and NO_(x) emissions.

[0010] Additional EPA requirements went into effect at the beginning of1995 which apply to urban buses equipped with engines manufactured priorto 1994. These requirements apply to engines in service when they comedue for rebuilding. Following engine rebuild the requirements must bemet. One portion of these requirements specifies that if technology canbe demonstrated for particulate reduction for these pre-1994 busengines, that technology would be mandated for use on those engines forwhich it is certified. Two tiers of such technology/emissions reductionattainment were promulgated including:

[0011] 1. Meet the 1994 Emissions Standard of 0.1 g/BHP-h TPM, with atechnology cost cap of about $8,000.

[0012] 2. Reduce Engine-Out TPM Emissions by at least 25%, with atechnology cost cap of about $3,000.

[0013] The first of the above attainment levels, which is considered thestricter of the two requirements, if demonstrated and certified, takesprecedence. Thus, the 25% TPM reduction tier was considered a“fall-back” position, if the 0.1 g/BHP-h TPM tier could not be met. Itis clear from the strict emissions requirements for new diesel enginesused in urban buses and the attainment requirement for pre-1994 busengines that a major challenge exists for this type of application.

[0014] Diesel engines used in urban bus applications in the U.S. are ofmany types, both two-cycle and four-cycle, supplied by a range of engineoriginal equipment manufacturers (OEM's). However, a large percentage ofurban transit buses have two-cycle engines from one manufacturer(Detroit Diesel Corp.). The emissions reduction system of this inventionis considered to be applicable to any diesel engine for loweringemissions and the level of emissions reduction attained is expected tobe dependent on the specific engine, its operating parameters andbaseline engine-out emissions. However, this invention has been found tobe especially useful for two-stroke diesel engines, and as demonstratedherein, can be used with such engines manufactured prior to 1994 tobring them into compliance with the 1994 particulate emissions standardof 0.1 g/BHP-h TPM, as discussed above.

[0015] Oxidation catalysts comprising a platinum group metal dispersedon a refractory metal oxide support are known for use in treating theexhaust of diesel engines in order to convert both HC and CO gaseouspollutants and particulates, i.e., soot particles, by catalyzing theoxidation of these pollutants to carbon dioxide and water. Suchcatalysts have generally been contained in units called diesel oxidationcatalysts (DOC's), or more simply catalytic converters or catalyzers,which are placed in the exhaust train of diesel power systems to treatthe exhaust before it vents to the atmosphere. However, by the time theexhaust gas reaches the catalyzer, it has generally lost a considerableamount of heat, both by radiation through the engine and exhaust systemwalls, and by intentional power transfer at the turbocharger. Becausethe efficiency of such catalytic oxidation processes is generally adirect function of the gas temperature, such temperature losses can havea significant negative impact on the effectiveness of the catalyzer.

[0016] One approach to improving the effectiveness of the catalyzer isto maintain the exhaust temperature at as high a level as possible, fromthe combustion chamber and through the connecting exhaust train to thecatalyzer. Heat-insulating structures and heat-insulating coatings,i.e., thermal barrier coatings have been employed by those skilled inthe art to enhance the thermal efficiency of internal combustion enginesby permitting more complete fuel burning at higher temperatures.Typically, such heat-insulating coatings have been applied to all of thechamber surfaces, including the cylinder walls and head and pistoncombustion faces to prevent heat loss. Heat-insulating structures andheat-insulating coatings have also been used in automobile exhaustsystems to maintain high exhaust temperatures required by thermalreactors and catalytic converters, thus reducing the emission ofunburned hydrocarbons emitted into the atmosphere as an undesirablecomponent of exhaust gas.

[0017] U.S. Pat. No. 5,384,200 is directed to particular thermal barriercoatings and methods of depositing such coatings on the surfaces ofcombustion chamber components. As discussed in that patent, insulatingthe combustion chamber components reduces the amount of heat loss in theengine. The higher temperature in the combustion chamber results in amore complete combustion of the fuel in the chamber, and also results ina hotter exhaust being delivered to any downstream catalytic convertersto promote more effective oxidation of the oxidizable components of theexhaust stream.

[0018] The use of thermal barrier coatings has also been suggested forengine components other than in-cylinder surfaces. In a paper entitled“High Performance Coatings for Diesels and Other Heat Engines”, by RoyKamo, presented at the Thermal Spray Coatings Conference, GorhamAdvanced Materials Institute, Orlando, Fla., on Sep. 12-14, 1993, it issuggested that engine performance can be improved by applying thermalbarrier coatings to various engine components. In addition toin-cylinder surfaces such as the piston crown and cylinder head, thearticle also suggests the exhaust port, exhaust manifold andturbocharger housing.

SUMMARY OF THE INVENTION

[0019] A typical diesel power system includes a diesel engine and anexhaust train through which the exhaust from the diesel engine passes.The present invention is directed to methods and apparatus for reducingthe total particulate matter emissions in said exhaust from the dieselengine. One embodiment of the method of the present invention comprisesthermally insulating at least a portion of the surface of the exhausttrain which comes into contact with the exhaust with a thermal barriercoating, and incorporating an oxidation catalyst into at least a portionof the thermal barrier coating in operative contact with the exhaust.This is accomplished by thermally insulating at least a portion,preferably the hottest portion of the exhaust train which carries thehot exhaust gas stream from the diesel engine to the atmospheric vent.The insulation is applied to surfaces of the exhaust train which are indirect contact with exhaust gas, that is, the inside surfaces of theexhaust train components. The oxidation catalyst is incorporated into atleast a portion of the thermal coating, and optionally intosubstantially all of the thermal coating.

[0020] Preferred oxidation catalysts for use in the present inventionare base metal oxides, particularly the rare-earth metal oxides, ormixtures of materials containing the base metal oxides or rare-earthmetal oxides. Preferred rare-earth oxide catalysts for use in thisinvention are praseodymium oxide and ceria. Good results are alsoobtained with other rare-earth oxides, as discussed further below. Thebase metal oxides can be used alone, or in combination with catalyticplatinum group metals, such as platinum, palladium and rhodium.

[0021] By insulating the exhaust train in accordance with the presentinvention, the effectiveness of the oxidation of the oxidizablecomponents of the exhaust is increased in a downstream diesel oxidationcatalyst (DOC) unit, and this decreases the level of undesirableemissions in the exhaust. Incorporating an oxidation catalyst into thethermal coating further reduces the emissions, particularly the TPMemissions. The catalyzed thermal barrier and the downstream DOC unitcombine for a significant reduction in the overall pollution level inthe exhaust.

[0022] Typically, the exhaust train of a diesel power system includes amanifold to collect the exhaust from the engine and channel it into oneor more exhaust pipes. Being closest to the engine, the manifold isgenerally the hottest section of the exhaust train. Therefore, in apreferred embodiment of the present invention, at least a portion of theinner surface of the manifold is insulated to reduce the amount of heatlost through the manifold walls and thus maintain the exhaust at hightemperature. Preferably, substantially the entire inner surface of themanifold is coated, that is at least about 90% of the area exposed tothe hot exhaust gases.

[0023] From the manifold, pipes carry the exhaust through variousapparatus which may be present in the exhaust train. Typically, aturbocharger is provided downstream of the manifold. Such devices arewell known to those skilled in the art. A turbocharger mechanicallyextracts power from the exhaust stream, such as by a compressor drivenby the exhaust, and transfers it to the inlet air stream to improve theoverall efficiency of the diesel power system. As a result of such powerextraction, the temperature of the exhaust gas generally dropssignificantly, such as about 100° F. or more, as it passes through theturbocharger. It is therefore a further preferred embodiment of thepresent invention not only to insulate the manifold, but also toinsulate the pipe or pipes connecting the manifold to the turbocharger,when a turbocharger is present.

[0024] After the exhaust exits the turbocharger, it is at a lowertemperature. Downstream of the turbocharger, many commercial dieselpower systems include a diesel exhaust oxidizer (DOC), as discussedabove, for oxidizing the oxidizable components of the exhaust stream.Generally, the hotter the exhaust is when it enters the catalyticoxidizer, the more effective the oxidizer is in oxidizing the harmfuloxidizable components. It is therefore a further embodiment of thepresent invention to insulate the pipes connecting the turbocharger tothe downstream catalytic oxidizer.

[0025] A further embodiment of the present invention is to combine theinsulative coating of the exhaust train, as discussed above, withinsulative coating of the surfaces of the combustion chamber components,in order to maximize the combustion of the fuel in the combustionchamber and to further impede heat loss from the exhaust stream. Thesurfaces to be coated can include the piston crown, the cylinder headand the valve faces, as well as any other surfaces which are exposed tothe combustion.

[0026] As discussed above, catalytic converters in diesel power systemsare located in the exhaust train, and the effectiveness of the catalystsin such converters is reduced by temperature loss in the exhaust train.In accordance with one aspect of the present invention the catalyticoxidation of oxidizable components in the exhaust stream is improved byproviding catalysts in the thermal barrier coatings which are applied tothe exhaust train. By providing the catalysts in the high temperatureend of the exhaust train, the catalysts are able to act on the exhaustgas when it is at its highest temperature. Furthermore, because suchoxidation is an exothermic reaction, it is possible that this catalyticoxidation may increase the temperature of the exhaust gas, thuspromoting more effective oxidation downstream at the catalyticconverter.

[0027] In another embodiment of the present invention, in which thediesel power system exhaust train includes a turbocharger, the method ofreducing the total particulate matter emissions in the exhaust simplycomprises providing an oxidation catalyst in the exhaust train betweenthe engine and the turbocharger. In this case, the oxidation catalystcan be mounted on the operating surfaces of a monolithic support, of thetype well known in the art. As discussed further below, the turbochargercan significantly reduce the temperature of the exhaust gases. Byproviding catalyst in the exhaust train prior to the turbocharger, thecatalytic oxidation can be conducted at the elevated exhausttemperatures before the turbocharger is reached. Optionally, the innersurfaces of the exhaust train can also be insulated, as discussed above.Also, if the surfaces are insulated, additional catalyst can beincorporated into a portion or substantially all of the insulation.

[0028] In a further embodiment of the present invention, when thecombustion chamber is provided with a thermal barrier coating, anoxidation catalyst is provided on or in such coating in the combustionchamber. Oxidation catalysts in the combustion chamber can promote morecomplete oxidation of the fuel, thereby decreasing the amount ofundesirable emissions sent to the exhaust train.

[0029] In a particular embodiment of the present invention, catalyticceramic coatings are applied to the in-cylinder surfaces of thecombustion chambers of an internal combustion engine, especially acompression ignition (diesel) engine. These coatings are of low thermalconductivity compared with standard metal parts, and provide a thermalbarrier at the combustion chamber walls which keeps heat in the cylinderand promotes more complete combustion of the fuel, thereby givinggreater fuel efficiency and lower emissions of particulates (SOF anddry-carbon/soot). In addition the coatings are provided with catalyticsurfaces which further promote combustion of unburned fuel andparticulates for increased efficiency and lower particulate emissions.

[0030] Another aspect of the present invention is that it was found thatproviding smooth and non-porous surface properties to the coatings, alsocontributes to improved combustion of unburned fuel and soot. This isbelieved to be the result of low drag at the surface which allows theswirl and mixing of the fuel. Such smooth and non-porous surfaces alsoreduce adsorption of the fuel which impacts the coated combustionchamber walls. Such adsorption can cause slow and incomplete combustion.The smoothness of thermal sprayed coated surfaces can be furtherimproved by sanding or polishing. The increased smoothness can furtherreduce drag at the surface and thereby improve the mixing and swirlingaction of the fuel-air mixture, which in turn leads to bettercombustion.

[0031] In a particular embodiment of the present invention a top coat ofmullite is used to protect the ceramic coating. The ceramic coatings areessentially the same as otherwise described herein for insulativecoatings, except that a top layer of an alumino-silicate (mullite)ceramic layer is provided. The layer should be at least about 2 milsthick, and preferably about 3 to 5 mils thick. Under this typically isthe yttria-stabilized zirconia layer and beneath that the bond coat.These coatings are therefore three layer coatings with an overallthickness approximately the same as the above coatings without mullite.The reason for the mullite top layer is to provide a very chemicallyinert ceramic surface with high resistance to the corrosive andaggressive materials encountered in the combustion and exhaust (sulfurand sulfates, calcium, zinc, nitrogen oxides and nitrates, chlorides,phosphorus, etc.). The “as sprayed” mullite top layer is less porous(about 3% porosity) than the zirconia layer, which is about 10%porosity.

[0032] The combustion chamber surfaces which are coated with thecatalytic materials, such as catalytic oxides, will be at least thecrowns (including the bowls of pistons which have bowls for receivinginjected fuel, as is well-known in the art). The exhaust valves andcylinder head fire decks can also be coated with the catalytic oxides.The overall coating thickness should be relatively thin, for example,less than about 20 mils. and preferably less than about 15 mils. Thesethicknesses are the total of all coatings, such as a bond coat, ceramicthermal barrier layer(s) and catalytic oxide layer(s). This thicknesscriteria is to produce a coating with good thermo-mechanical propertiesand which will exhibit good long-term durability in-cylinder.

[0033] Another aspect of this invention is the use of stainless steelbond coats, particularly martensitic steels, to give good durabilitywhen the coatings are applied to aluminum alloy surfaces. Aluminum alloypistons are used in many internal combustion engines, thus the need forthe special bond coat. The typical alloy bond coats used with priorthermal spray coatings have been comprised of MCrAlY alloys where M=Ni,Co, Fe, etc., as is well-known in the art. In accordance with thepresent invention, stainless steel, particularly martensitic stainlesssteel, such as type 431 SS, has been found to be particularly useful asa bond coat to bond ceramics, such as yttria stabilized zirconia, toaluminum substrates.

[0034] It is believed that the reason such stainless steels areeffective as bond coats is related to the relative coefficients ofthermal expansion (CTE) of the components. Aluminum has a CTE of about23.0, and aluminum alloys have CTE's in the general range of about 21 to25. The ceramic thermal barrier coatings have CTE's of roughly about 6to 8, with standard 7% yttria stabilized zirconia being about 7.6. Thestainless steels used in the present invention, particularly martensiticstainless steels, have relatively low CTE's, which approximate those ofthe ceramic thermal barrier coatings. Such steels are commonly referredto as being “low-shrink”, because of their relatively low CTE. At thesame time, such stainless steels also bond well to the aluminumsubstrate. It is believed that the use of a stainless steel which has acoefficient of expansion relatively close to that of the ceramiccoatings acts to keep the ceramic firmly adhered to the aluminum. TheCTE of type 431 SS martensitic stainless steel is about 6.6, which iseven less than that of the yttria stabilized zirconia used as thethermal barrier coating in some of the examples below. The stainlesssteel bond coat does not move differentially to the zirconia ceramic,and remains firmly anchored to the aluminum substrate. As a result, thetendency for the coating to crack and spall off such aluminum substratesis greatly reduced

[0035] A further aspect of the present invention is providing animproved diesel oxidation catalyst (DOC) unit in the exhaust train. Theimproved DOC unit more effectively oxidizes the oxidizable components ofthe exhaust stream, thus reducing the TPM level of the exhaust. Theimproved DOC unit comprises a metal monolithic catalyst support ratherthan a ceramic support as used in other units.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a schematic representation of a diesel power system.

[0037]FIG. 2 is an illustrative graphical printout of a combinedthermogravimetric/differential thermal analysis (TGA/DTA) for an activecatalyst, in this case containing ceria.

[0038]FIG. 3 is a printout of a TGA/DTA for relatively inert cordierite.

[0039]FIG. 4 is a comparative bar graph of different configurations ofthe present invention and comparative baseline data.

[0040]FIG. 5 is a graph showing the comparative effects of the injectiontiming setting on TPM and NO_(x) emission levels.

DETAILS OF PREFERRED EMBODIMENTS

[0041] A simple, generalized schematic of a diesel power system 10 suchas is used in commercial buses is depicted in FIG. 1. Diesel fuel iscombusted in one or more cylinders 13 of diesel engine 12. The exhaustfrom diesel engine 12 is collected in exhaust manifold 14 and channeleddownstream by one or more pipes 16. The exhaust train of such dieselsystems generally includes a turbocharger 18, which extracts power fromthe exhaust and transfers it to the air intake of the engine 12 by meanswhich are well known in the art. After turbocharger 18, pipe 20 carriesthe exhaust downstream to an optional diesel oxidation catalyst (DOC)unit 22, or more simply a catalyzer, in which a catalyst is provided topromote the oxidation of harmful emissions contained in the exhaust.Downstream of catalyzer 22 pipe 24 carries the exhaust to a muffler 26from which the exhaust exits through pipe 28 to the atmosphere.Optionally and preferably, catalyzer 22 and muffler 26 are combined intoa single catalyzer/muffler unit, thus eliminating the need for twoseparate units and intermediate connecting pipes.

[0042] The exhaust gas exiting engine 12 is at elevated temperature, andcools as it passes through the exhaust train. In particular, when aturbocharger is present, the temperature of the gas is significantlyreduced by the process which transfers power to the inlet air. Thetemperature drop across the turbocharger can be in excess of about 100°F. In any case, as the exhaust gas moves through the manifold and downthe exhaust train to the atmosphere, the gas loses heat through thewalls of the exhaust train by radiation or other heat transfer means.

[0043] In accordance with a preferred embodiment of the presentinvention, an insulative layer 30 is provided on the inner surface of atleast a portion of the exhaust train. Although insulative layer 30 isshown on the inside of manifold 14, turbocharger 18 and connecting pipes16, 20, 24 and 28, it is not necessary for all of these surfaces to becoated to achieve the desired improvement in the oxidation of theoxidizable exhaust components. The exhaust gas is generally at itshottest temperature when it leaves the engine, and it is more effectiveto insulate the hottest components of the exhaust train to maintain theexhaust at the highest possible temperature. Therefore, it is preferredto at least insulate part of the manifold, more preferably substantiallythe entire manifold, that is, at least about 90% of the surface exposedto the exhaust gas. When a turbocharger is in the system, it is alsopreferable to insulate the pipe 16 connecting the manifold to theturbocharger. After the exhaust gas passes through the turbocharger, itis at a significantly lower temperature, therefore insulating the pipingdownstream of the turbocharger is not as significant to the overallimprovement of oxidation efficiency. Because one of the purposes ofinsulating the exhaust train is to increase the effectiveness of thecatalyzer unit 22, there is little to be gained in regard to emissionscontrol by insulating the exhaust train downstream of the catalyzer.

[0044] In one embodiment of the invention, an oxidation catalyst isincorporated into at least a portion of the thermal insulative coating30. Preferably, the catalyst is provided in the highest temperatureregions of the exhaust stream, that is in the manifold 14 and the pipe16 connecting the manifold to the turbocharger 18. The catalyst can bedisposed on selected portions of the insulated surface 30, or onsubstantially all (that is, at least about 90%) of the insulatedsurface.

[0045] Optionally, a separate oxidation catalyst unit 32 may be providedupstream of the turbocharger. This unit can include a monolithiccatalyst support, as is well known in the art, on which the oxidationcatalyst is disposed. Such a catalyst unit can be provided in place ofincorporating catalyst into coating 30, or can be in addition tocatalyzed coating 30. When a catalyst unit 32 is provided, it is notnecessary to insulate the exhaust train with coating 30. However,preferably at least the exhaust manifold 14 and the connecting pipe 16are insulated, as discussed above.

[0046] Optionally, the inner surface of the cylinders 13 can also becoated with either catalyst, thermal barrier insulation, or catalystincorporated into thermal barrier insulation, as discussed above. Thepreferred sites for coating in-cylinder are the piston crown 34 or thecylinder head 36, also known as the firedeck, and valve faces. Whencoating in-cylinder, appropriate adjustments would also have to be madeto maintain the desired compression, as would be understood by oneskilled in the art.

[0047] The preferred catalysts are oxidation catalysts which can combustthe hydrocarbons (referred to as SOF or VOF) and carbonaceous materials(referred to as insolubles or soot) which make up nearly all of thetotal particulate mass (TPM) emitted in the exhaust of diesel engines.The catalysts used for this invention include base metal oxides withactivity for burning SOF and/or insolubles. These oxides can be used incombination with one another, or also optionally in combination withprecious metals (e.g. Pt, Pd, Rh, etc.), to get enhancement in overallactivity some cases. Test results demonstrating relative performance ofdifferent base oxides and their combinations are given below.

[0048] The base metal oxide combustion catalysts can be used in and witha diesel engine system in a number of ways for destroying SOF andinsolubles, thereby reducing TPM emissions.

[0049] The catalysts can be used within the combustion chambers of thediesel engine. They can be applied to the combustion chamber surfaces,including the piston crowns, valve faces and firedeck area of thecylinder heads. These are surfaces which can come into contact with SOFand insolubles which can be burned there. This is especially true of thepiston crowns which are known to encounter impingement of at least aportion of the fuel or partially burned fuel directly on their surfacesfollowing fuel injection. In addition, optical observations have shownhigh concentrations of soot at the outside of the flame and near thepiston crown surfaces. The catalysts can be applied directly to thecombustion chamber surfaces as a coating or they can be applied onto thesurface of another coating which as already been put onto the combustionsurfaces, such as a thermal barrier coating. This can have an addedbenefit in that the thermal barrier coating can keep heat in thecylinder and provide a surface to keep the catalyst hot and thereby moreactive, plus it can provide a stable, compatible surface for applyingthe oxide catalyst. The catalysts could be applied to the abovementioned surfaces by a variety of means known to the art including:impregnation with a solution of soluble precursor followed by thermal orchemical decomposition to obtain the active oxide, thermal sprayingprocesses such as flame spraying or plasma spraying of the oxidecatalysts or their precursors, or by application of a slurry of thecatalyst material together with appropriate binders, if needed, followedby thermal treatment to dry, cure and set the catalyst coating.

[0050] The catalysts can also be applied as a coating, in manners suchas those described above, to the internal surfaces of the exhaust systemof the engine, including the ports in the cylinder heads, exhaustmanifolds, exhaust pipes and turbocharger housing. As discussed above,the exhaust is significantly cooled as it passes through a turbocharger.Therefore, the catalysts are especially useful in the exhaust systemsections prior to the exhaust reaching the turbocharger, where theexhaust temperature is at its highest, thereby providing the mostsensible heat for enhanced catalyst activity. As with the in-cylindercoatings above, the catalyst can be applied directly to the innersurfaces of the exhaust system components or applied to the surface ofanother coating, e.g. a thermal barrier coating, which has already beenput onto the surfaces. The benefits of incorporating the catalyst intothe surface of the thermal barrier coating would be the same as thosedescribed in regard to in-cylinder usage above.

[0051] In some engines, such as Detroit Diesel's 6V92TA, there is arelatively long run of exhaust manifolds and piping connecting theexhaust ports with the turbocharger. This particular engine has sevensections of connecting pipes, including two exhaust manifolds (it's aV-configuration engine), two connector pipes, one from each manifold,which feed into a Y-connector, which in turn is connected to aturbo-extension pipe, which finally connects to an elbow connector,which is connected to and feeds the combined engine exhaust to theturbocharger. This pre-turbo exhaust system not only provides arelatively large interior geometric surface area onto which to put acatalyst coating, as described above, but also has several straight runsof piping with sufficient inner diameter which could be fitted orconfigured with a catalyst coated flow-thru honeycomb substrate, such asthat depicted as component 32 in FIG. 1 and discussed above.

[0052] Such a separate catalyzed honeycomb unit 32 can provide a muchgreater geometric surface area for contacting the catalyst with theexhaust, thereby enhancing overall effectiveness and activity for TPMreduction. For example, the turbo connector pipe noted above has aninner diameter of 3.31″ with a length of 11.38″ which could accommodatea flow-thru catalytic element. Such a catalyst would be near the engineexhaust port, and before the turbocharger. This would provide for highertemperatures for the catalyst and thereby better activity and more rapid“light-off” after initial engine “start up”, these terms being wellknown in the art, for burning the VOF and insoluble components of theTPM's. A metallic monolithic flow-thru honeycomb would be an especiallygood candidate as a substrate to place in a such a high temperature andpressure position, because of good mechanical strength and relativelylow pressure drop. Another advantage of a metallic substrate is thatthey are typically made by wrapping corrugated metal foils in layersfrom the inside out, thereby allowing the fabrication of practically anydiameter substrate to fit any inner diameter of exhaust piping. Theoxide catalysts, possibly in combination with one or more preciousmetals, can be coated onto the metallic flow-thru substrate as awashcoat by conventional techniques, including dip-coating or flowcoating. The preferred catalytic materials for use in the configurationsdescribed above have been defined, at least initially, by laboratorytesting which is described below.

Laboratory Testing

[0053] The identification of candidate catalysts and ceramic coatingmaterials was first determined by laboratory testing. A test wasdeveloped to screen various materials for their capabilities to catalyzethe combustion of diesel particulates. For the test, the dieselparticulates were simulated by a mixture of lube oil (model SOF) andcarbon black (model soot). The lube oil and carbon black were mixed inthe ratio of 30:70 to approximate their proportions in representativediesel particulate emissions. The lube/carbon black mixture was furthercombined with a powdered sample of the candidate catalyst material inthe ratio of 20 parts model particulate and 80 parts catalyst to form auniform, intimate mixture. The performance of the candidate catalyst forburning the admixed model particulates was evaluated using athermogravimetric/differential thermal analysis unit (TGA/DTA; STA 1500,Polymer Labs). In a given test run a small sample (e.g., 30 mg) of thecatalyst/model particulate mixture was placed in the sample pan of theTGA/DTA and heated in a flow of air from ambient temperature to about1000° C. at a ramp rate of 20° C./min. The TGA/DTA unit was used tosimultaneously measure the weight loss and heat evolution from the testsample as a function of temperature. The test was conducted with anatmosphere of flowing air to simulate the lean environment found indiesel exhaust.

[0054] The results from a representative test run of a candidatecatalyst are shown in FIG. 2. The sample weight loss (TGA, lower trace)exhibits two breaks at different temperatures. The lower temperaturebreak (about 240-343° C.) is due to the loss of the lube oil(volatilization +combustion), and the higher temperature break (about617-713° C.) is due to the combustion of the carbon black. The heatevolution (DTA, upper trace) due to combustion of lube and carbon blackare seen as separate peaks (exotherms) in the curve at about 358° C. and687° C., respectively. All catalyst candidates exhibited the two breaksfor weight loss in the TGA trace as the lube and carbon black wereburned, respectively. However, some catalyst candidates exhibited littleor no activity for burning the lube oil and as a result exhibited no DTApeak in the lube oil temperature range and all the lube oil loss was dueto volatilization alone. This can be seen in FIG. 3 for cordieritepowder, an inert material, which was mixed with the model particulatemixture and run in air. As can be seen, cordierite is completelyinactive for burning lube oil and the weight loss in the temperaturerange of 236° C. to 334° C. is due entirely to volatilization of thelube.

[0055] The carbon black is a nonvolatile solid and thus all samplesexhibited a DTA peak in the carbon black temperature range due tocombustion. As can be seen, even with an inert material such ascordierite a carbon black DTA peak is obtained, as shown in FIG. 3.

[0056] Catalyst candidates differed in performance for burning the lubeand carbon black, as evidenced by the temperatures at which the lube oiland carbon black combustion occurred. For the screening tests the figureof merit was taken as the temperature of the inflection in the weightloss curve (maximum rate of weight loss) and the temperature of the peakin the DTA curve (maximum rate of heat evolution from combustion). Thebest candidate catalyst materials were those which exhibited the lowesttemperatures of TGA inflection and DTA peak for the combustion of lubeand carbon black. That is, the best catalyst materials shift the burningof lube or carbon black to the lowest possible temperature. This can beseen for carbon black burning by comparing the DTA Peak temperature forthe catalyst candidate run in FIG. 2 (687° C.) to that for cordierite inFIG. 3 (708° C.)

[0057] The catalyst candidates screened in this test procedure weremainly metal oxides, although non-oxides are within the scope of thisinvention and similar screening tests can be performed on representativesamples. In addition, oxides or non-oxides in combination with one ormore precious metals is considered within the scope of the invention.

[0058] Pure metal oxides were tested and mixtures of metal oxides weretested. For the latter some were based on candidate catalytic metaloxides impregnated onto low surface area, non-active oxides via solutionimpregnation from a water soluble precursor followed by calcination inair. The metal oxides chosen have been of both low and high surface areaand were tested in powder form as described above. The low surface areaoxides were of special interest because for this invention the formenvisioned is of a ceramic coating applied to metal substrates such aspiston crowns, valves, cylinder heads, exhaust manifolds and exhaustpipes by methods such as thermal spray techniques (plasma or HVOFspraying), and as a result lower or very low surface area coatings areexpected to result. These coating techniques are known to givethermo-mechanically stable and highly adherent coatings which would beneeded for the in-cylinder parts. Higher surface area oxides are alsoconsidered because of the potential to apply them to the substrate byslurry or wet coating processes. This could be done for the exhaustpipes which are exposed to less extreme thermo-mechanical conditionsthan are in-cylinder parts. Furthermore, both high surface area and lowsurface area oxides or ceramic materials would be candidates forcatalysts to be used in enhancing TPM insolubles or dry carbon burningin diesel oxidation catalyst units or catalyzed diesel soot filters.

[0059] Test results for a series of candidate oxides and mixed oxidesystems are given in Table I. In Table I, the TGA inflectiontemperatures and DTA peak temperatures are given for each candidate, andthe results showed significant variations for different candidates. Forpurposes of the present invention, the lowest possible temperature isdesired for DTA peak and TGA inflection. As will be shown by the resultspresented below, it is of particular importance for the catalyst toaffect the combustion of the carbon component of the TPM, because thedownstream diesel oxidation catalyst units have been found to be muchmore effective on the VOF component than on the dry soot. Therefore, thebest candidate catalysts for use in the present invention are those withthe lowest DTA inflection and TGA peak temperatures for carbon blackcombustion. These results indicated that praseodymium oxide (Pr₆O₁₁)showed a significant ability to decrease the TGA and DTA values for drycarbon burning, especially Samples 21 and 23-27.

[0060] High surface area cerium oxide (Sample 20) also showed very goodcombustion characteristics (low TGA and DTA values) for carbon blackburning. In addition, this cerium oxide (Sample 20) also was the bestfor burning the lube oil component of the model particulates (i.e.,lowest DTA peak temperature). As can be seen from Table I, samples ofcerium oxide with lower surface areas (e.g., Sample 16 with SA=0.9 m²/gand Sample 17 with SA=8.9 m²/g) did not exhibit as low TGA and DTAvalues for carbon black combustion as did Sample 20. This shows thatwith ceria, surface area, and specifically high surface area, isimportant for obtaining the best activity for carbon black combustion,as well as lube oil combustion. Thus, high surface area cerium (orcerium containing) oxides are included as preferred catalysts.

[0061] Praseodymium oxide, also a preferred catalyst, can be seem formTable I to be highly active for carbon black combustion. Furthermore,praseodymium oxide is highly active with a low surface area (3.7-23m²/g, Samples 23-25). Thus, surface area of praseodymium oxide is not asimportant a factor for high carbon black combustion activity as is forceria. However, praseodymium oxide does not exhibit as high an activityfor lube oil combustion. TABLE I Laboratory TGA/DTA Test Results withVarious Oxides for Lube Oil & Carbon Black Combustion in Air TGAInflection DTA Peak Temp. (° C.) Temp. (° C.) SA Lube Lube SampleCatalyst (m²/g) Oil Carbon Oil Carbon 1 alpha-Alumina 8.9 287 697 388687 (Al₂O₃) 2 Mullite <1 278 688 None 698 (alumina-silica) 3 CordieritePowder <1 284 694 None 708 4 Chromium Oxide 2.9 294 649 387 651 (C₂O₃)279 637 407 625 5 Yttrium Oxide 10.3 290 685 371 707 (Y₂O₃) 6 Zirconia(ZrO₂, 0.4 286 641 None 632 Yttria Stabilized) 7 Lithium Niobate 0.9 291687 None 712 8 Niobium(V) Oxide 1.7 290 712 399 699 (Nb₂O₁₀) 9 TerbiumOxide 1.2 303 660 300 693 (Tb₆O₁₁) 10 Europium Oxide 5.6 306 665 353 667(Eu₂O₃) 11 Samarium Oxide 1 301 669 337/ 703 (Sm₂O₃) 394 12 Tantalum(V)Oxide 0.3 288 679 331 680 (Ta₂O₁₀) 13 Ceria (CeO₂), 280 687 382 718 7 wt% on Mullite 14 Ceria (CeO₂), 292 664 358 687 7 wt % & Pt 0.1 wt % onMullite 15 Ceria (CeO₂), 271 637 344 604 10 wt % Citrate Process & Pt0.1 wt % on Cordierite 16 Ceria (CeO₂) 0.9 289 703 403 728 99.9% 17Ceria (CeO₂) 90% 8.9 307 646 369 638 18 Ceria (CeO₂) 96% 282 677 406 67119 Ceria (CeO₂) 96% 290 703 None 709 After Plasma Spraying 20 Ceria(CeO₂) 99% 165 252 584 236 541 21 Praseodymium 275 653 410 662 Oxide(Pr₆O₁₁) 7 wt % on Mullite 22 Pr₆O₁₁ (10 wt % 284 692 390 708 CitrateProcess & Pt 0.1 wt % on Cordierite) 23 Pr₆O₁₁ 4 297 593 285/ 572 399 24Pr₆O₁₁ (96%) 3.7 303 612 445 581 25 Pr₆O₁₁ (HSA) 23 299 565 317/ 540 41426 Pr₆O₁₁ (HSA) with 277 591 328 564 1 wt % Pt 27 Pr₆O₁₁ (96%) after 306607 386 591 HVOF spraying 28 CeO₂ (96%) & 293 693 336 693 Pr₆O₁₁ (96%)mixed in 70:30 ratio then plasma sprayed

EXAMPLES

[0062] The emissions reduction system which constitutes the presentinvention was tested and demonstrated by engine tests conducted using atwo-cycle diesel urban bus engine. The tests were conducted inaccordance with the U.S. Heavy Duty Transient Federal Test Procedure(FTP), defined in 40 CFR, Part 86, Subpart N (1995), incorporated hereinby reference. The FTP outlines the specific requirements for setting up,mapping and running a test engine for the performance and emissionsevaluation. A standardized 20-minute transient test cycle was used,including rapid changes of speed and torque which the engine mustproduce. The tests were run using 1994 emissions grade #2 diesel fuel(0.05 wt % S). Both cold start (after an overnight equilibrium soakperiod) and hot start transient tests were run and the data collected.Composite results,of both cold and hot start transients were reportedfor certification purposes. The composite results were calculated as aweighted average of the cold start (1/7) and hot start (6/7) transientresults as required by the FTP. For some engine configurations only hotstart transient data were collected to assess the relative contributionof the components comprising that configuration. The key resultsincluded determination of brake specific emissions (TPM, NO_(x), gasphase HC's and CO) and TPM breakdowns (insolubles, VOF) expressed ing/BHP-h. Engine fuel consumption was also determined (lb/BHP-h).

The Test Engine and Test Strategy

[0063] The test engine was a MY 1987 DDC 6V-92TA MUI (Serial #6VF120195), which was a 6 cylinder, two-cycle diesel engine with aV-configuration and having a displacement of 9.05 liters (552 cu. in.).The engine was turbocharged, aftercooled and had mechanical governingand mechanical unit fuel injectors. This engine is typical of those usedin a large proportion (about 40%) of urban transit buses. The enginedeveloped about 294 HP at 2100 RPM.

[0064] The engine was rebuilt and configured to give various test casesfor evaluation using the U.S. HD Transient Test (FTP). Theseconfigurations (examples) included the components of the currentinvention, as well as, other configurations (examples), including abaseline, for comparative purposes. The exhaust system used for testingand included the fittings for incorporation of the exhaust catalyst(DOC) into the exhaust train. The DOC element was located, for thesetests, 6 feet downstream of the exhaust manifold. The engine was run ona break-in cycle for at least 75 hours prior to the tests.

[0065] Fuel injection timing for the engine was controlled by theinjector “height” setting and was varied in the tests from 1.460″ to1.520″ with the greater injector height being a more retarded injectionconfiguration. Most of the test runs were done at an injection settingof 1.466″. The throttle delay for the tests was set at 0.594″.

[0066] Ceramic Coatings: The catalyzed and non-catalyzed ceramiccoatings used in the examples below to demonstrate the invention aredescribed below:

[0067] 1. Non-catalyzed Insulative Coatings: These coatings, referred toas “Coating A”, are basic ceramic coatings applied to a metal surfacevia the plasma spray process, as are well-known in the art. The plasmasprayed coatings were applied by Engelhard Surface Technologies in EastWindsor, Conn. Such coatings consist of:

[0068] a. A metal alloy bond coat (e.g. super alloy or 431 SS) whichacts as an interlayer between the metal surface of the part and theceramic layer. Particularly good results are obtained using a well-knownclass of metal-chromium-aluminum-yttrium alloys, commonly referred to asMCrAlY alloys, wherein the metal is preferably nickel, cobalt, iron orcombinations thereof. Such alloys are well known in the art, as forexample, in U.S. Pat. No. 5,384,200, cited above and incorporated hereinby reference.

[0069] b. An yttria-stabilized zirconia ceramic layer (e.g. 7-20 wt %yttria) deposited on top of the bond coat.

[0070] The coatings used for the present invention are relatively thin(<15 mils thick) compared with those typically used in the art (>60 milsthick). This gives them better thermo-mechanical stability and therebygood durability to survive the temperature gradients and stressesencountered in the combustion chamber of the engine. The bond coat layerfor these coatings is typically 3-5 mils thick with the remaindercomprising the yttria stabilized zirconia. The porosity of theyttria-stabilized zirconia can be controlled by adjusting the plasmaspray parameters, but typical for this application is about 10%porosity.

[0071] 2. Non-catalyzed Mullite Insulative Coatings: These coatings havethe same basic structure as the above non-catalyzed insulative coatings,except that the top-most 3-5 mils thickness is comprised of analumino-silicate (mullite) ceramic layer. Under this is theyttria-stabilized zirconia layer and beneath this is the bond coat.These coatings are therefore three layer coatings with an overallthickness approximately the same as the above coatings without mullite.The reason for the mullite top layer is to provide a very chemicallyinert ceramic surface with high resistance to the corrosive andaggressive materials encountered in the combustion and exhaust (sulfurand sulfates, calcium, zinc, nitrogen oxides and nitrates, chlorides,phosphorus, etc.). The “as sprayed” mullite top layer is less porous(about 3% porosity) than the zirconia layer, which is about 10%porosity. In the following examples, the mullite non-catalyzedinsulative coating is designated “Coating B”, and comprises the samefirst two layers as Coating A, with a mullite top coat.

[0072] The non-catalyzed mullite insulative coating used in the examplesbelow and identified as “Coating B” comprised a nominal 4 mil thick bondcoat of NiCrAlY alloy and a nominal 7 mil thick ceramic layer of 8%yttria stabilized zirconia. On top of the ceramic layer, a nominal 2 milthick layer of mullite was deposited.

[0073] 3. Catalyzed Insulative Coating: These coatings are catalyzedversions of the above non-catalyzed or mullite non-catalyzed insulativecoatings. The specific catalyzed coating used in the examples belowconsisted of the above Coating B applied by a plasma spray process whichhad been impregnated with a candidate metal oxide catalyst, and isdesignated “Coating C”. In this case the catalytic metal oxide waspraseodymium oxide (Pr₆O₁₁) which was applied to the Coating B surface(and pores) via an aqueous solution of praseodymium nitrate precursor,followed by drying and thermal decomposition of the nitrate to thecorresponding oxide. This was done in three applications to achieve apraseodymium oxide loading equivalent, for example, to about 0.25 g ofPr₆O₁₁ on the surface of a coated piston crown. The praseodymium oxidecatalyst was chosen as a candidate because of promising performance forburning dry carbon and to an extent SOF in model TGA/DTA lab tests.However, for the purposes of the present invention a variety ofcatalysts can be used, including other base metal and rare earth oxides,as well as, precious metals.

[0074] For all of the coatings, the surface of the metal part to becoated was first pretreated by grit blasting. This resulted in a clean,corrosion-free and roughened surface to insure good adhesion andmechanical interlocking of the plasma sprayed bond coat to the metalpart.

[0075] Ceramic (catalyst) Coated Parts: The engine parts coated withceramic (catalyzed) coatings for these tests included the following:

[0076] 1. Piston Crowns: The pistons for these tests were standardcommercial parts. The specific pistons initially had a compression ratioof 15:1. The top rim was relieved to avoid interference with thecylinder head coatings. The pistons were of a open bowl, low swirlprofile. The piston crowns were plasma spray coated with Coatings A orB. Application of the plasma spray coating changed the dimensions andbowl volume of the piston crown slightly, thus the coated pistons werecalculated to have a compression ratio of about 17:1. One set of CoatingB coated pistons had the catalyst (praseodymium oxide) applied to make aset of Coating C coated pistons. The catalyst constituted a very thincoating and thus did not change the relative compression ratio of thepistons.

[0077] 2. Engine Heads & Valves: The coatings were applied by the plasmaspray process to the area of the engine cylinder heads enclosed by thecombustion chambers (“fire deck”). During the coating process theexhaust valves were installed in the heads and seated. In this way boththe “fire deck” region and the exhaust valve faces could be plasma spraycoated simultaneously with Coatings A or B. One set of heads and valveswhich had been coated with Coating B had the catalyst (praseodymiumoxide) coating applied to make a set of Coating C coated heads andvalves. The exhaust ports on these heads had also been plasma spraycoated with Coating B but did not have the praseodymium coating appliedin that area of the head.

[0078] 3. Exhaust Manifolds and Pre-Turbo Pipes: The plasma sprayprocess is a line-of-sight process and as such it can be used to coat apart as long as the area of the part to be coated is accessible to thespray stream of the plasma spray gun. It is thus possible to spray theinterior of parts, such at tubes and pipes, as long as the inner surfaceis accessible. Larger tubes (e.g. >about 2″ id) can be coated througheach end for lengths of up to 1-2 ft. Smaller tubes can be coated on theinside using special mini-guns or mini-torches. The plasma spray processcan not; however, be used to coat around acute corners or in areas whichcan not be made accessible. The exhaust manifolds and pre-turboconnecting pipes for the DDC 6V92TA engine were large enough in diameterand straight enough that it was possible to coat the inner surface to asignificant extent (about 75%) with the plasma spray coating of CoatingB. One set of exhaust manifolds and pre-turbo pipes coated with CoatingB had the catalyst (praseodymium oxide) also applied to make a setcoated on the inner surface with Coating C.

[0079] The Exhaust Catalyst (DOC): A diesel oxidation catalyticconverter is comprised of a catalyst coating, typically composed of amixture of catalytically active base metal oxides and optional preciousmetals applied to the flow channel surfaces of a suitable monolithichoneycomb substrate. This substrate with the catalyst washcoat appliedis contained within a metal canister (the can) designed to hold thesubstrate in place and allow for the flow of the exhaust gases from theengine to pass over the catalyst.

[0080] Current Production DOC (DOC-A): A current production catalyst forthis application, designated “DOC-A” was obtained for comparativetesting. This catalyst was coated onto an extruded cordierite ceramichoneycomb catalyst substrate measuring 9.5″ dia.×6″ long. The cellspacing was 200 cpsi, with a wall thickness of 12 mil. The geometricsurface area was 13 m². The total catalyst washcoat loading was 2.95g/in³, for a total of 1254 g. The catalyst washcoat consisted of abottom coat of 1.00 g/in³ highly milled high surface area (150 m²/g)alumina, with a pore volume of 0.5 cc/g. The topcoat included the samealumina (1.05 g/in³) plus high surface area (150 m²/g)aluminum-stabilized ceria (0.90 g/in³), having a pore volume of 0.1cc/g, with platinum at 10 g/ft³ distributed equally on the alumina andceria in the topcoat. This catalyst was broken-in (de-greened) on theengine overnight before testing.

[0081] Improved DOC (DOC-B): The improved catalyst used for thisinvention, designated “DOC-B” is comprised of high surface area, highpore volume bulk metal oxides of aluminum and cerium which in turncontain platinum impregnated on their surfaces. This catalyst was coatedonto a metallic wrapped foil honeycomb substrate with the dimensions of10.5″ dia.×6″ long. The cell spacing was 310 cpsi, with a wall thicknessof 4 mil. The geometric surface area was 27 m². Such substrates aremanufactured in Sweden by EcoCat, a subsidiary of Sandvik Steel, and aremade in accordance with one or both of U.S. Pat. Nos. 4,633,936 and5,085,268, both of which are incorporated herein by reference. As withDOC-A, the total catalyst loading was 2.95 g/in³, but in this case for atotal of 1534 g. The catalyst coating consisted of: [1] A thin “etchcoat” of highly milled high surface area (150 m²/g) alumina to insuregood adherence of the catalyst washcoat to the metallic honeycombsurface; [2] An undercoat consisting of high surface area alumina mixedwith high surface area aluminum-stabilized ceria (150 m²/g) in a ratioof 34:66 by weight; and [3] A topcoat consisting of very high surfacearea and pore volume alumina (250-300 m²/g) mixed with high surface areaaluminum-stabilized ceria in a ratio of 54:46 by weight, and havingplatinum impregnated onto the alumina and ceria at about 0.3% by weightof the topcoat loading with the platinum distributed equally on thealumina and ceria in the top coat. This catalyst DOC-B was prepared andcoated onto the metallic honeycomb substrate. The loading levels forthis catalyst were as follows:

[0082] 1. Etch coat of 0.20 g/in³ highly milled high surface areaalumina

[0083] 2. Bottom coat of 0.60 g/in³ of the high surface area aluminaplus 0.20 g/in³ of the high surface area ceria.

[0084] 3. Topcoat of 1.05 g/in³ of the very high surface area aluminaplus 0.90 g/in³ of the high surface area ceria and containing 10 g/ft³platinum distributed about 90% on the alumina and about 10% on the ceriain the topcoat.

[0085] The catalyst coated substrate was then put into a canister andbroken in (de-greening) on a diesel engine for 40 hours prior to thetests.

[0086] Test Configurations: The DDC 6V92TA MUI engine was set up withvarious configurations of ceramic (catalyzed) coatings and with andwithout aftertreatment catalysts (DOC's) to demonstrate the currentinvention and assess the relative contributions of the variouscomponents of the invention. The various configurations included: [A]Coated or uncoated piston crowns; [B] Coated or uncoated heads & valves;[C] Coated and uncoated exhaust manifolds and pre-turbo exhaust pipes;[D] Insulated exhaust pipes between the turbo-outlet and the exhaustcatalyst (DOC); [E] Presence or absence of the exhaust catalyst (DOC) inthe exhaust stream and [F] Type of exhaust catalyst (DOC), improved orproduction. The configurations (examples) tested are given in TABLE IIwhich shows 9 Examples plus baselines. The examples are summarized asfollows:

Example 1

[0087] The engine configuration which includes catalyzed Coating C onthe piston crowns, heads and valves and in the exhaust manifolds andpre-turbo pipes, plus insulated exhaust pipes between the turbo-outletand the DOC and with the improved diesel oxidation catalyst DOC-B.

Example 2

[0088] Same as Example 1 but using the production exhaust catalyst DOC-Ainstead of the improved DOC-B.

Example 3

[0089] Same as Example 1 but with stock, uncoated heads and valves.

Example 4

[0090] Same as Example 1 but without the insulation on the exhaust pipesbetween the turbo-outlet and the DOC.

Example 5

[0091] Same as Example 1 but with stock, uncoated exhaust manifolds andpre-turbo exhaust pipes.

Example 6

[0092] Same as Example 5 but without a diesel oxidation catalyst (DOC)in the exhaust stream.

Example 7

[0093] The engine configuration which includes non-catalyzed Coating Bon the piston crowns, heads and valves and in the exhaust manifolds andpre-turbo pipes, plus the improved DOC-B.

Example 8

[0094] Same as Example 7 but with stock, uncoated exhaust manifolds andpre-turbo exhaust pipes.

Example 9

[0095] Same as Example 8 but without a diesel oxidation catalyst (DOC)in the exhaust stream.

Baseline

[0096] The current engine rebuilt to its baseline condition for a 1979DDC 6V92TA MUI and without coatings or a diesel oxidation catalyst (DOC)in the exhaust stream.

[0097] Baseline ('94)

[0098] This is included for comparison purposes and refers to DDC 6V92TAMUI baseline engines tested in 1994. The engine was rebuilt to a 350 HPrating and again to a 277 HP rating with rebuild kits representative ofa MY 1985 engine.

[0099] Test Results: The results of transient emissions tests for theconfigurations corresponding to the Examples listed in TABLE II aboveare given in TABLE III. The first column in TABLE III refers to theengine test configuration (Examples). The second column gives thethrottle delay setting in inches (0.594″ in each case here). The thirdcolumn gives the injection timing used for the individual test run orset of test runs. The next column designates the type of HD transienttest (cold start, hot start or composite). The next four columns givethe brake specific emissions for gas phase HC's, CO, NO_(x) and TPM,respectively. The next two columns give the breakdown of the TPM intoinsolubles and VOF components. The final column gives the brake specificfuel consumption for the test run.

[0100] In addition to the data in TABLE III the results for hot starttransient tests for the examples are shown graphically in the bar chartin FIG. 2. These hot start results are all for the 1.466″ fuel injectiontiming setting. FIG. 2 gives the average particulate emissions for eachexample, either as TPM or particulate breakdowns into insoluble and VOFportions, where available. As will be discussed further below in regardto the specific examples, catalyzed coatings in the exhaust train,particularly in the exhaust manifold and pre-turbo pipes, areparticularly effective for reducing the insoluble soot component of thetotal particulate matter (TPM) emissions.

[0101] Results for Example 1, an example of the present invention, aregiven in TABLE III for injection timing settings from 1.460″ to 1.520″(most retarded injection). As can be seen the 0.1 g/BHP-h TPM standardwas readily met for injection settings of 1.460″, 1.466″ and 1.475″. Asthe injection was progressively retarded the TPM emission levelincreased, but only slightly, and TPM emissions from 0.076 to 0.084g/BHP-h were achieved. The technology used for the Example 1configuration achieved dramatically lower TPM emissions compared withthe baseline engine configurations with timing setting of 1.466″ from1994 tests. The baseline engines gave TPM emissions of at least 0.200g/BHP-h. In the current tests retarding the injection timing wasaccompanied by reduction in NO_(x) emissions. For Example 1 withinjection timing settings of 1.466″ and 1.475″ lower NO_(x) emissionswere achieved (10.11 and 8.97 g/BHP-h, respectively) than for the 194baseline engine configurations (10.3 to 11.7 g/BHP-h) while maintainingTPM emissions well below the 0.1 g/BHP-h standard. The level of NO_(x)emission could be reduced even further to 5.07 g/BHP-h (essentially the1994 NO_(x) emission standard) by additional retarding of injectiontiming to 1.520″. This was accompanied by a level of TPM emissions(0.141 g/BHP-h) which exceeded the 0.1 g/BHP-h standard. However, it wasstill lower than the TPM emissions level from the baseline engine (>0.2g/BHP-h). The relationship of both TPM and NO_(x) emissions levels forExample 1 as a function of injection timing setting is shown graphicallyin FIG. 4. Example 1 with injection timing setting in the range of1.466″ to 1.475″ appears to best fulfill the goals of meeting the 0.1g/BHP-h TPM emissions with good NO_(x) emissions levels. The TPMbreakdown for Example 1 (1.466″) showed 0.049 g/BHP-h insolubles and0.031 g/BHP-h VOF showing that this configuration gave substantialreduction in both fractions compared with the baseline results. Thebrake specific fuel consumption for Example 1 was found to be comparableor lower than that of the '94 baseline engine configurations showingthat implementation of the technology of this invention is notaccompanied by a fuel efficiency penalty.

[0102] The results for Example 2 show that when the larger volume (8.5liter), improved DOC-B of this invention (on 10.5″ dia.×6″ long 310 cpsimetallic substrate) was replaced with the smaller volume (7.0 liter)production DOC-A (on 9.5″ dia.×6″ long 200 cpsi ceramic substrate), theTPM emissions increased to 0.116 g/BHP-h and the 0.1 g/BHP-h standardcould not be achieved. It, therefore, appears that the improved catalystexhibited a TPM emissions performance advantage of 0.037 g/BHP-hcompared with the production catalyst. Although the TPM breakdown forExample 2 has not yet been determined it is expected that the improvedcatalyst gives higher VOF conversion than the production catalystbecause of its improved washcoat properties and larger catalyst volume.The NO_(x) emissions levels with the two catalysts were comparable. Gasphase HC emissions were about 20% lower with the improved catalyst.However, CO emissions were slightly higher, possibly due to partialoxidation of the greater relative amount of VOF and gas phase HC'sconverted by the improved catalyst. The brake specific fuel consumptionfor Example 2 was comparable with Example 1. These results show that theimproved DOC-B and larger catalyst volume are key components for thebest performance of the invention.

[0103] The results for Example 3 show that the engine configuration withthe uncoated heads and valves run with an injection timing setting of1.460″ exhibited slightly higher levels of emissions than for Example 1with coated heads and valves run at the same injection timing setting.The TPM emissions for Example 3 were ca 0.014 g/BHP-h higher than forExample 1. The composite NO_(x) emission levels of Examples 3 and 1 werecomparable for the 1.46″ timing setting. However, gas phase HC's and COwere slightly higher for Example 3 than for Example 1. This indicatedthat the configuration with coated heads and valves was better foremissions performance, but the 0.1 g/BHP-h TPM emission goal could stillbe met with uncoated heads and valves and the configuration of Example 3would be simpler and lower in cost from a manufacturing point of view.Thus Example 3 might be considered useful under some circumstances. Thecomposite brake specific fuel consumption for Example 3 appears to beslightly lower than for Example 1, but this could be within theexperimental error of the measurement.

[0104] For Example 4 the insulation was removed from the exhaust pipesbetween the turbo-outlet and the diesel oxidation catalyst(DOC). Thecold start TPM emission result for Example 4 was about 15% higher thanthe cold start results for Example 1 showing the positive effect of theinsulation on reducing emissions for the cold start test condition. Theaverage hot start TPM emissions for Example 4 were also found to beslightly higher showing that the insulation has a positive overalleffect on particulate emissions. TPM breakdowns show slightly higherinsolubles and slightly lower VOF for Example 4 compared with Example 1.The reason for this is not fully understood, but could be related toinhibition of the development of insoluble related components in thehotter insulated exhaust pipes (Examples 1 & 3) compared with theun-insulated exhaust pipes (Example 4). The results for Example 4 showthat it was not necessary to have the insulation in place to meet the0.1 g/BHP-h TPM emission standard, but its beneficial effect can give aslightly greater delta TPM to allow for greater DF and better operationunder cold ambient conditions. Composite NO_(x) emission levels werecomparable for Example 4 and Example 1. Surprisingly, gas phase HC andCO emissions were slightly lower without the insulation. The fuelconsumption was comparable both with and without the insulation.

[0105] For Example 5 the Coating C coated exhaust manifolds andpre-turbo exhaust pipes of Example 1 were replaced with stock, uncoatedmanifolds and pre-turbo exhaust pipes. The test results showed that theTPM emission level for this configuration was substantially higher(0.121 g/BHP-h) than when the coated manifolds and pipes were used(0.080 g/BHP-h). The TPM performance advantage with the coated manifoldsand pipes appears to be 0.041 g/BHP-h. Comparison of the TPM breakdownsfor Examples 1 & 5 shows that the key contribution of the use of CoatingC coated exhaust manifolds and pre-turbo pipes is in reduction in theinsoluble portion of the particulates. The level of NO_(x) emissions forExample 5 was comparable with that of Example 1 as was the brakespecific fuel consumption levels. For Example 5 gas phase HC emissionswere slightly lower and CO emissions were slightly higher than forExample 1. These results show that the coated exhaust manifolds andpre-turbo pipes were an important component contributing to theperformance of the system which constitutes this invention. This was asurprising result in that intuitively one would not consider the innersurface of the exhaust manifolds and pipes as potentially having mucheffect on emissions considering the relatively low surface area.However, there are considerable changes in flow direction as the exhaustpasses through the manifolds and pipes and the momentum of components ofthe particulates (VOF aerosols, dry carbon particles and carbonparticles with adsorbed VOF) might cause them to impact on the innerwalls at pipe bends and angle changes, thus allowing for interactionwith the ceramic (catalyzed) coatings and burning.

[0106] For Example 6 the configuration consisted of Coating C coatingsin the combustion chamber only. The coated exhaust manifolds andpre-turbo exhaust pipes were replaced with stock, uncoated manifolds andpipes as with Example 5, plus the diesel oxidation catalyst (DOC) wasremoved. The test results showed relatively high TPM emissions level forthis configuration (0.188 g/BHP-h), compared with Example 5 andespecially compared with Example 1. Compared with Example 5, it appearedthat the TPM emissions performance advantage with the diesel oxidationcatalyst (DOC) was 0.067 g/BHP-h. Compared with Example 1, it appearsthat the TPM emissions performance advantage for the coated exhaustmanifolds and pre-turbo pipes plus the diesel oxidation catalyst was atotal of ca 0.108 g/BHP-h. The TPM breakdown for Example 6 shows thatnearly all of the increased TPM emission compared with Example 5 was dueto greater VOF contribution. This is consistent with the high VOFremoval performance observed with the DOC present. Comparing Example 6with the baseline engine configurations indicates that the TPM emissionsperformance advantage for the combustion chamber coatings alone wasabout 0.012-0.013 g/BHP-h. The emission levels of NO_(x) and brakespecific fuel consumption for Example 6 were comparable with those forExamples 1-5 at the equivalent injection timing setting.

[0107] The results of these tests show that substantial reduction in TPMemissions for a 2-cycle DDC 6V92TA MUI bus engine can be dramaticallyreduced and the 0.1 g/BHP-h TPM standard can be met with the technologydescribed in this invention record. The key components of the inventionappear to be the improved diesel oxidation catalyst (DOC), the ceramic(catalyzed) coatings on the inner surfaces of the exhaust manifolds andpre-turbo exhaust pipes and the ceramic (catalyzed) coatings on thecombustion chamber surfaces (piston crowns, heads and valves). Each ofthese components has its own incremental effect on reducing the drycarbon and VOF portions of the TPM emissions. We believe that thecombination of components used to achieve these results provides asystem capable of significant reduction in TPM emissions from dieselengines. This coupled with the possibilities of reducing NO_(x) viainjection retard without great increases in TPM emissions gives a systemto address the two key emissions challenges for diesel engines, namelyTPM and NO_(x).

NO_(x) Benefits

[0108] The NO_(x) and TPM trade-off is well known in industry. Eachdiesel engine model will produce a set of NO_(x) and TPM emissionsdepending on the engine parameters. This set of NO_(x) and TPM valuescan be plotted as shown in FIG. 5, which is a representation of thevalues reported for Example 1, in Table III, compared to the Baseline(350 HP) values. Engineers calibrate engines to achieve the desiredbalance of NO_(x)-TPM emissions by adjusting various engine operatingparameters. The primary engine parameter is the timing of fuelinjection, which is the time during the cycle at which diesel fuelbegins to enter the combustion chamber. Retarding the injection (i.e.,starting injection later in the cycle) has the well-known effect ofreducing NO_(x) at the expense of increasing TPM. The results depictedin FIG. 1 show that the system of the present invention cansignificantly reduce NO_(x) levels with only a relatively small increasein TPM emissions. TABLE II Description of Emissions Control SystemsTested Pre-Turbo Insulated Head & Manifold & Post-Turbo Piston ValvePipes Exhaust Coating Coating Coating Pipes Catalyst Example 1 Coating CCoating C Coating C Yes DOC-B Example 2 Coating C Coating C Coating CYes DOC-A Example 3 Coating C None Coating C Yes DOC-B Example 4 CoatingC Coating C Coating C No DOC-B Example 5 Coating C Coating C None YesDOC-B Example 6 Coating C Coating C None Yes None Example 7 Coating BCoating B Coating B No DOC-B Example 8 Coating B Coating B None No DOC-BExample 9 Coating B Coating B None No None Baseline None None None NoneNone Baseline None None None None None (′94) (277 & 350 HP)

[0109] TABLE III Summary of HD Transient Engine Emissions Tests ThrottleInjection Transient Measured Emissions (g/BHP-h) TPM Breakdown BSFCDelay (″) Timing (″) Test Type HC CO NOx TPM Insolubles VOF (lb/BHP-h)Ex. 1 0.594 1.46 Cold-3 0.172 0.401 10.65 0.076 0.458 Hot-4 0.161 0.25410.93 0.077 0.058 0.019 0.44 Hot-5 0.162 0.275 11.06 0.079 0.438 Comp.0.162 0.274 10.89 0.077 0.442 0.594 1.466 Cold-4 0.219 0.524 9.94 0.0760.043 0.033 0.453 Hot-8 0.154 0.422 10.14 0.08 0.049 0.031 0.436 Hot-90.173 0.431 10.09 0.081 0.049 0.032 0.431 Comp. 0.163 0.436 10.11 0.080.049 0.031 0.438 0.594 1.475 Hot-6 0.17 0.309 8.97 0.089 0.054 0.030.442 0.594 1.52 Hot-19 0.1 0.31 5.07 0.141 0.122 0.019 0.449 Ex. 20.594 1.466 Hot-15 0.201 0.41 10.32 0.116 0.081 0.035 0.439 Ex. 3 0.5941.46 Cold-2 0.215 0.481 10.3 0.089 0.042 0.047 0.457 Hot-2 0.203 0.42210.91 0.092 0.046 0.046 0.425 Hot-3 0.208 0.473 10.89 0.092 0.045 0.0470.43 Comp. 0.205 0.43 10.83 0.091 0.046 0.046 0.429 Ex. 4 0.594 1.466Cold-5 0.17 0.48 9.8 0.083 0.457 Hot-16 0.154 0.359 10.17 0.08 0.0540.026 0.433 Hot-20 0.15 0.51 10.22 0.09 0.065 0.025 0.441 Hot-21 0.150.49 10.21 0.089 0.439 Comp. 0.15 0.51 10.16 0.09 0.443 Ex. 5 0.5941.466 Hot-17 0.135 0.509 10.1 0.121 0.094 0.027 0.437 Ex. 6 0.594 1.466Hot-18 0.358 1.298 10.2 0.188 0.108 0.08 0.439 Ex. 7 0.594 1.46 Hot-3110.7 0.097 0.079 0.018 1.47 Hot-29 0.16 0.59 9.87 0.102 0.083 0.0190.436 1.485 Hot-32 7.8 0.14 0.128 0.015 1.5 Hot-33 6.5 0.18 0.157 0.019Ex. 8 0.594 1.47 Hot-40 0.185 0.81 9.72 0.116 0.0974 0.0186 0.441 Ex. 90.594 1.47 Hot-39 0.413 1.481 9.84 0.191 0.441 Baseline 0.594 1.466 ColdHot Hot Comp. Baseline 0.594 1.466 Cold 0.5 0.9 10.3 0.2 0.07 0.13 0.441(′94) Hot 0.5 1.6 10.3 0.21 0.08 0.13 0.422 350 HP Comp. 0.5 1.5 10.30.21 0.08 0.13 0.424 Baseline 0.636″ 1.466″ Cold 0.5 1.7 11.6 0.24 0.494(′94) Hot 0.5 0.8 11.7 0.2 0.451 277 HP Comp. 0.5 0.9 11.7 0.2 0.457

Example 10

[0110] This example illustrates the incremental improvement of emissionsperformance (particularly particulate emissions) obtained within-cylinder thermal barrier coating and more so with catalyzed thermalbarrier coatings. This effect was shown by engine emissions testingusing the U.S. Heavy Duty Transient Test Procedure, as previouslydiscussed.

[0111] A 1986 DDC 6V92-TA MUI engine was rebuilt using standard rebuildkit parts. This engine was built to a 294 HP configuration, and fittedwith 9F-80 fuel injectors and 17:1 compression ratio pistons. The enginewas run with a fuel injection timing setting of 1.460″ (injector heightin inches) and a throttle delay of 0.636″ (throttle actuator adjustmentin inches). The engine was equipped with a standard exhaust system andno after treatment catalyst was used. In this way the baselineengine-out emissions of a standard engine rebuild were evaluated. Theengine was broken in for the required 100 hrs and then tested foremissions in hot start transient test runs.

[0112] Next the engine was rebuilt again, but was equipped withuncatalyzed thermal barrier coatings (the above “Coating B”) on allpiston crowns, the head firedecks and exhaust valve faces. (The inletvalves, which are located in the cylinder side walls of this enginerather than in the head, were not coated.) This engine, also 294 HP, wasfitted with 9F-80 fuel injectors and the compression ratio with thecoatings was 17:1 as with the standard rebuild, above. This coatedengine was also run with a fuel injection timing setting of 1.460″ and athrottle delay of 0.636″. This engine was run with the same standardexhaust system as used for the standard rebuild, above. the engine wasbroken in for 100 hrs and tested for emissions performance in hot starttransients.

[0113] Next the engine was rebuilt again, but this time it was equippedwith catalyzed thermal barrier coatings (the above “Coating C”) on allpiston crowns, the firedecks and valves. The catalyst was Pr₆O₁₁ asdescribed previously for “Coating C”. This engine was built to a 294 HPconfiguration with 9F-80 fuel injectors and compression ratio of 17:1 aswith the standard rebuild and uncatalyzed thermal barrier coatingrebuild, discussed above. The engine was equipped with the same standardexhaust train used for the standard build and uncatalyzed thermalbarrier coated engines, above. This engine was broken in and tested foremissions performance in hot start transient tests.

[0114] As is apparent for the three engine builds described above, asmuch care was taken as possible to have the builds be identical and theengines run in the same way with the only key variable being thein-cylinder, combustion chamber surface coatings.

[0115] The emissions results of the hot start transient tests for thethree engine builds described above are shown in TABLE IV below: TABLEIV Engine Configuration Emissions (g/BHP-h) and Run No. HC CO NOx PMStandard Rebuild 1 0.50 1.45 11.44 0.193 2 0.50 1.47 11.50 0.194 3 0.511.57 11.28 0.200 4 0.51 1.56 11.15 0.195 Avg. 0.51 1.51 11.34 0.196 ±0.003 Uncatalyzed Coating (“Coating B”) 1 0.58 1.21 11.05 0.185 2 0.581.23 10.90 0.188 3 0.58 1.17 11.10 0.185 Avg. 0.58 1.21 11.05 0.186 ±0.001 Catalyzed Coating (“Coating C”) 1 0.57 1.04 10.70 0.170 2 0.581.13 10.70 0.176 Avg. 0.58 1.09 10.70 0.173 ± 0.003

[0116] As can be seen the average particulate emissions level of theengine coated with the uncatalyzed coating (“Coating B”) was lower thanthe average particulate emissions level of the standard rebuild engineby 0.010 g/BHP-h. Furthermore, the average particulate emissions for theengine coated with the catalyzed coating (“Coating C”) was lower thanaverage particulate emissions for the engine coated with the uncatalyzedcoating (“Coating B”) by 0.013 g/BHP-h. The emissions ranges (average ±2sigma) for each of these engines do not overlap and thus aresignificantly different. These results show that the catalyzed coatingsgive a real and distinct effect in reducing the particulate emissionsfor the diesel engine.

Example 11 Stainless Steel Bond Coats

[0117] Experiments were conducted to test thermal barrier coatings forresistance to rapid thermal cycling using various bond coats for bondinga standard 7% yttria stabilized zirconia ceramic top coat to an aluminumsubstrate, simulating the conditions to which an aluminum piston wouldbe exposed in operation in a diesel engine. Based on manufacturesliterature, the ceramic is considered to have a coefficient of thermalexpansion (CTE) of about 7.6, while the aluminum substrate has a CTE ofabout 23.0. A “thermal cycle machine” was developed to perform thetests. The device was made to move a test sample between a heat sourceand a cooling flow for a programmable period of time in order tosimulate typical engine run conditions. In the case of the evaluation ofaluminum piston bond coats, a three-inch diameter disk sample is used.This is coated on one face with the bond coat and ceramic top coatsystem for the purpose of seeing if the top coat will remain adherent tothe bond layer. The heat source is a large propane air burner whoseflame impinges directly on the coated disk. Cooling is done by a highvolume compressed air flow. In operation the test disk is shuttled backand forth between the heat and cool locations for timed durations thatallow a range of 900° F. (high) to 200° F. (low) to be reached. A cyclewas developed in which a 2.5 minute dwell in each station achieved thetarget temperatures.

[0118] Four bond materials were chosen for this experiment. In eachcase, the bond coat was applied by plasma spraying the metal in powderform onto the aluminum disk. The materials tested were Nichrome®(80%Ni/20%Cr) alloy (Metco 43C), having a CTE of about 7.3; 95%nickel/5% aluminum alloy (metco 480), having a CTE of about 10; NiCrAlY(Praxair 211), having a CTE of about 13.0; and type 431 martensiticstainless steel (Metco 42C), having a CTE of about 6.6. For each sample,the number of thermal cycles to failure was measured. For purposes ofthis test, coating failure is considered when the top coat beginschipping and separating from the bond coat. The Nichrome sample failedafter 47 cycles; the nickel/aluminum sample after 83 cycles; the NiCrAlYsample after 23 cycles; and the stainless steel sample still had notfailed after 123 cycles, at which time the test was discontinued. Thisshowed the distinct improvement obtained by using a stainless steel bondcoat under simulated engine conditions to bond a ceramic coat toaluminum, particularly a “low-shrink” martensitic steel such as type 431SS.

We claim:
 1. In a diesel power system which includes a diesel engine andan exhaust train through which the exhaust from the diesel enginepasses, a method of reducing the total particulate matter emissions insaid exhaust from the diesel engine comprising: a) thermally insulatingat least a portion of the surface of said exhaust train which comes intocontact with said exhaust with a thermal barrier coating; and b)incorporating an oxidation catalyst into at least a portion of thethermal barrier coating in operative contact with the exhaust.
 2. Themethod of claim 1 wherein said exhaust train includes an exhaustmanifold mounted on said engine for receiving the exhaust from saidengine, wherein the step of thermally insulating comprises insulating atleast a portion of the surface of the manifold which comes into contactwith the exhaust, and the oxidation catalyst is incorporated into atleast a portion of the surface of the manifold which is thermallyinsulated.
 3. The method of claim 2 comprising insulating substantiallyall of the surface of the manifold which comes into contact with theexhaust, and the oxidation catalyst is incorporated into substantiallyall of the surface of the manifold which is thermally insulated.
 4. Themethod of claim 2 wherein the exhaust train further comprises aturbocharger mounted downstream of the manifold and operationallyconnected to said manifold by a connecting pipe, and wherein the step ofthermally insulating comprises insulating at least a portion of thesurfaces of both the manifold and the connecting pipe which come intocontact with the exhaust.
 5. The method of claim 4 comprising insulatingsubstantially all of the surfaces of the manifold and the connectingpipe which come into contact with the exhaust.
 6. The method of claim 5wherein the oxidation catalyst is incorporated into substantially all ofthe surfaces of the manifold and connecting pipe which are thermallyinsulated.
 7. The method of claim 1 wherein the step of thermallyinsulating comprises insulating substantially all of the surface of theexhaust train which comes into contact with the exhaust from where theexhaust exits the diesel engine to a preselected point downstream on theexhaust train.
 8. The method of claim 7 further wherein the oxidationcatalyst is incorporated into substantially all of the surface which isthermally insulated.
 9. The method of claim 1 wherein the diesel enginecomprises one or more cylinders having combustion chambers wherein themethod further comprising thermally insulating the inner surfaces of thecombustion chamber with a thermal barrier coating.
 10. The method ofclaim 8 further comprising incorporating an oxidation catalyst into thethermal barrier coating of the combustion chamber in operative contactwith the gases therein.
 11. The method of claim 1 wherein said oxidationcatalyst comprises a base metal oxide.
 12. The method of claim 11wherein said oxidation catalyst comprises a rare-earth metal oxide. 13.The method of claim 12 wherein said oxidation catalyst comprisespraseodymium oxide, cerium oxide or combinations thereof, or a mixedoxide containing praseodymium, cerium or combinations thereof.
 14. In adiesel power system which includes a diesel engine and an exhaust trainthrough which the exhaust from the diesel engine passes, and wherein theexhaust train comprises a turbocharger, a method of reducing the totalparticulate matter emissions in said exhaust from the diesel enginecomprising providing an oxidation catalyst in said exhaust train betweenthe engine and the turbocharger, wherein the oxidation catalyst is inoperative contact with the exhaust.
 15. The method of claim 14 whereinthe oxidation catalyst is deposited on at least a portion of the surfaceof said exhaust train between the engine and the turbocharger whichcomes into contact with said exhaust.
 16. The method of claim 15 whereinthe oxidation catalyst is deposited on substantially all of the surfaceof said exhaust train between the engine and the turbocharger whichcomes into contact with said exhaust.
 17. The method of claim 14 whereinthe oxidation catalyst is mounted on the surface of a monolithicsupport.
 18. The method of claim 17 further comprising thermallyinsulating at least a portion of the surface of said exhaust trainbetween the engine and the turbocharger which comes into contact withsaid exhaust with a thermal barrier coating.
 19. The method of claim 18comprising thermally insulating substantially all of the surface of saidexhaust train between the engine and the turbocharger which comes intocontact with said exhaust with a thermal barrier coating.
 20. The methodof claim 18 further comprising incorporating an oxidation catalyst intoat least a portion of the thermal barrier coating in operative contactwith the exhaust.
 21. The method of claim 14 wherein said oxidationcatalyst comprises a rare-earth metal oxide.
 22. The method of claim 21wherein said oxidation catalyst comprises praseodymium oxide, ceriumoxide or combinations thereof, or a mixed oxide containing praseodymium,cerium or combinations thereof.
 23. In a diesel power system whichincludes a diesel engine and an exhaust train through which the exhaustfrom the diesel engine passes, a system for reducing the totalparticulate matter emissions in said exhaust from the diesel enginecomprising: a) a thermal barrier coating on at least a portion of thesurface of said exhaust train which comes into contact with saidexhaust; and b) an oxidation catalyst incorporated into at least aportion of the thermal barrier coating in operative contact with theexhaust.
 24. A diesel engine exhaust manifold comprising a thermalbarrier coating on at least a portion of the inner surface of saidmanifold and an oxidation catalyst incorporated into at least a portionof the thermal barrier coating, said catalyst located to be in operativecontact with an exhaust stream passing through the manifold.
 25. In adiesel engine having one or more cylinders which have combustionchambers, a catalyzed thermal barrier coating for the surfaces ofcomponents of the combustion chambers comprising: a) a thermal barriercoating deposited on the surfaces of said components; and b) anoxidation catalyst which is provided at the surface of the thermalbarrier coating.
 26. The catalyzed thermal barrier coating of claim 25wherein the oxidation catalyst is incorporated into the thermal barriercoating.
 27. The catalyzed thermal barrier coating of claim 25 whereinthe oxidation catalyst is coated onto the thermal barrier coating. 28.The catalyzed thermal barrier coating of claim 25 wherein saidcomponents are selected from the group consisting of the piston crowns,cylinder heads, and valves.
 29. The catalyzed thermal barrier coating ofclaim 25 wherein the oxidation catalyst comprises a base metal oxide.30. The catalyzed thermal barrier coating of claim 29 wherein theoxidation catalyst comprises a rare-earth metal oxide.
 31. The catalyzedthermal barrier coating of claim 30 wherein the oxidation catalystcomprises praseodymium oxide, cerium oxide or combinations thereof, or amixed oxide containing praseodymium, cerium or combinations thereof. 32.In a diesel engine having one or more cylinders which have combustionchambers, a method of reducing the total particulate emissions in theexhaust from the diesel engine comprising: a) depositing a thermalbarrier coating on the surface of components in the combustion chambers;and b) providing an oxidation catalyst at the surface of said thermalbarrier coating.
 33. The method of claim 32 wherein the oxidationcatalyst is incorporated into the thermal barrier coating.
 34. Themethod of claim 32 wherein the oxidation catalyst is coated onto thethermal barrier coating.
 35. The method of claim 32 wherein the coatingis deposited on components of the combustion chamber selected from thegroup consisting of the piston crowns, cylinder heads, and valves. 36.The method of claim 32 wherein the oxidation catalyst comprises a basemetal oxide.
 37. The method of claim 36 wherein the oxidation catalystcomprises a rare-earth metal oxide.
 38. The method of claim 37 whereinthe oxidation catalyst comprises praseodymium oxide, cerium oxide orcombinations thereof, or a mixed oxide containing praseodymium, ceriumor combinations thereof.
 39. An improved ceramic thermal barrier coatingfor a metallic substrate in which the improvement comprises a mullitetop coat.
 40. The ceramic thermal barrier coating of claim 35 comprisinga bond coat on the metallic substrate, an yttria stabilized zirconiaintermediate coat, and the mullite top coat.
 41. The ceramic thermalbarrier coating of claim 36 in which the bond coat comprises an MCrAlYalloy.
 42. The ceramic thermal barrier coating of claim 36 in which thebond coat comprises a martensitic stainless steel.
 43. The ceramicthermal barrier coating of claim 30 further comprising an oxidationcatalyst provided at the surface of the mullite top coat.
 44. A methodof protecting a ceramic thermal barrier coating comprising depositing amullite top coat onto the ceramic thermal barrier coating.
 45. Themethod of claim 44 wherein the thermal barrier coating comprises a bondcoat on the metallic substrate and an yttria stabilized zirconiaintermediate coat onto which the mullite top coat is deposited.
 46. Themethod of claim 44 further comprising providing an oxidation catalyst atthe surface of the mullite top coat.
 47. A thermal barrier coating foran aluminum substrate comprising a stainless steel bond coat depositedon the aluminum substrate and a ceramic thermal barrier coatingdeposited on the stainless steel bond coat.
 48. The coating of claim 47wherein the stainless steel is martensitic.
 49. The coating of claim 48wherein the stainless steel is a type 431 martensitic stainless steel.50. The coating of claim 47 wherein the ceramic thermal barrier coatingdeposited on the stainless steel is an yttria stabilized zirconia.
 51. Amethod of bonding a ceramic coating to an aluminum substrate comprisingdepositing a bond coat of stainless steel on the aluminum substrate, andthen depositing a top coat of the ceramic on the bond coat.
 52. Themethod of claim 51 wherein the stainless steel is martensitic.
 53. Themethod of claim 52 wherein the stainless steel is a type 431 martensiticstainless steel.
 54. The method of claim 51 wherein the bond coat isdeposited by thermal spraying.
 55. The method of claim 51 wherein theceramic is an yttria stabilized zirconia.